Alcudia Valley


Main commodities: Zn Pb Ag Cu
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The Alcudia valley in Ciudad Real Province of southern Spain contains a large number of Pb-Zn-Ag-Cu deposits hosted by Neoproterozoic and Palaeozoic sediments which have been mined since Roman times.   The most significant of the mineralisation is related to two phases of deformation and granite emplacement in the Hercynian Orogeny.   The metals, sulphur and carbon in the deposits has been sourced from the host rocks.

The host sequence commences with Neoproterozoic (Riphean) greywackes and black shales unconformably overlain by Riphean to Vendian sandstones, conglomerates, shales and limestones.   These are unconformably followed by a sequence of interbedded quartzites, sandstones, siltstones, black shales, mudstones and minor limestones from Ordovician to late Craboniferous in age, with a number of unconformities and associated conglomerates.

Five types of deposit are recognised, as follows:
1). Minor stratabound, disseminated Zn>Pb sulphides and small veins within Ordovician limestone with associated strong silicification and dolomitisation,
2). Strongly deformed syntectonic veins (to mylonitic textures) in Hercynian D1 fractures within Ordovician rocks (sandstones, siltstones, black shales and quartzites) with Zn>Pb, strike lengths of up to 1.1 km and thicknesses of 1 m, persisting down dip for up to 150 m, as quartz sulphide veins grading out to vein networks and stringers to strongly silicified (and weakly chloritised) country rock.   The vein mineralogy comprises pyrite, sphalerite, galena, chalcopyrite and quartz.   These are the second most important of the vein types, accounting for 12% of the production.
3). Small to moderate sized veins within Hercynian D1 and D2 fractures cutting upper Ordovician and Silurian rocks (siltstones and black shales), rarely exceeding 100 m in length, with widths of 0.15 to 5 m and down dip extents of 50 m.   These range from breccia bodies to well defined veins with only weak wall rock alteration (silicification, carbonatisation and chloritisation).   The primary mineralogy comprises sphalerite, galena, quartz and carbonate, with sphalerite > galena.
4). Syntectonic Zn-Pb veins restricted to Neoproterozoic black shales and greywackes, with strike lengths of 25 to 500 m, 0.5 to 4 m thickness and up to 110 m depth extents within Hercynian D2 strike slip shears.   The vein mineralogy comprises sphalerite, galena, quartz ±carbonate
5). Post tectonic Pb-Zn veins, widely distributed throughout the district, but most commonly in Neoproterozoic rocks influenced by Hercynian D2 deformation.   These are the most important veins, accounting for 70% of the veins and the bulk of the production.   They vary from a few metres to more than 2 km in strike length, a few cms to more than 15 m in thickness, while the deepest workings have been to 700 m below surface.   They mostly trend in a northeasterly direction and are tensional or less commonly trans-tensional open spaces in shear fractures.   Wall rock alteration is mainly carbonate and chlorite, with minor silicification and sericitisation.   The vein assemblage includes galena, sphalerite, chalcopyrite, ankerite and barite with galena and ankerite being dominant.

Total historic production from the valley is estimated to be 1.4 Mt of Pb (1.25 Mt from 1840 to 1988) and 350 t Ag.   No relaible Zn tonnage is available.

For more detail see the reference(s) listed below.

The most recent source geological information used to prepare this summary was dated: 2003.    
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd.   Unauthorised copying, reproduction, storage or dissemination prohibited.

  References & Additional Information
   Selected References:
Palero F J, Both R A, Arribas A, Boyce A J, Mangas J, Martin-Izard A  2003 - Geology and metallogenic evolution of the polymetallic deposits of the Alcudia Valley Mineral Field, eastern Sierra Morena, Spain: in    Econ. Geol.   v98 pp 577-605

Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge.   It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published.   While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo takes no responsibility what-so-ever for inaccurate or out of date data, information or interpretations.

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